Back: Measure length of pet’s back from the base of the neck to the base of the tail. See below for estimating by breed.Neck: Measure the circumference of pet’s neck for a snug fit. No need to add inches as you would with a collar.Chest/Girth: Measure girth around the broadest part of the chest and add 2”.Note: If the dog has a stout build, select one size larger.